As described in Patent Document 1, at the time of grinding of a highly accurate gear, gear grinding process is conducted such that while a thread-shaped grinding wheel is rotated around an axial center thereof and fed in an axial center direction, a position coming into contact with abrasive grains is changed by performing a grinding feed in a direction parallel to an axial center of a gear blank and by serially rotating the gear blank around the axial center in proposed continuous-generation gear grinding.
This continuous-generation gear grinding exclusively employs water-insoluble grinding fluid easily permeating a grinding point between the thread-shaped grinding wheel and the gear blank and excellent in washing performance of removing chips from a grinding wheel surface. For the continuous-generation gear grinding, the water-insoluble grinding fluid with low viscosity is recommended that has, for example, kinetic viscosity of 10 m2/sec (40° C.) or less so as to facilitate the permeation through the grinding point. However, a low-viscosity mineral oil contained in such a water-insoluble grinding fluid has high inflammability and may catch fire particularly under grinding conditions elevating the temperature of the grinding point and the chips. Therefore, it has been desired to switch the grinding fluid used in the continuous-generation gear grinding from the water-insoluble grinding fluid to water-soluble grinding fluid.